Preparation of phosphorus pentafluoride and fluorophosphoric acids

ABSTRACT

PHOSPHORUS PENTAFLUORIDE AND FLUOROPHOSPHORIC ACIDS ARE PREPARED FROM A FLUORINE SOURCE SELECTED FROM FLUOROSULFONATE FLUORIDES AND MIXTURES OF FLUORIDES AND FLUOROSULFONATES AND A PHOSPHORUS SOURCE SELECTED FROM PHOSPHORIC ACID AND MONO- OR DI-FLUOROPHOSPHORIC ACID. BY AN ANALOGOUS PROCESS, ARSENIC PENTAFLUORIDE AND FLUOROARSENIC ACIDS ARE PREPARED BY FLUORINATING AN ARSENIC SOURCE SELECTED FROM ARSENIC ACID AND MONOFLUOROARSENIC ACID.

United States Patent 3,769,387 PREPARATION OF PHOSPHORUS PENTAFLU- ORIDE AND FLUOROPHOSPHORIC ACIDS Robert A. Wiesboeck, Stone Mountain, and John D. Nickerson, Atlanta, Ga., assignors to United States Steel Corporation No Drawing. Continuation-impart of application Ser. No. 848,119, Aug. 6, 1969, which is a continuation-in-part of application Ser. No. 702,547, Feb. 2, 1968, both now abandoned. This application Mar. 24, 1971, Ser.

Int. Cl. C0111 25/10 US. Cl. 423-301 17 Claims ABSTRACT OF THE DISCLOSURE Phosphorus pentafluoride and fluorophosphoric acids are prepared from a fluorine source selected from fluorosulfonate fluorides and mixtures of fluorides nad fluorosulfonates and a phosphorus source selected from phosphoric acid and monoor di-fluorophosphoric acid. By an analogous process, arsenic pentafluoride and fluoroarsenic acids are prepared by fluorinating an arsenic source selected from arsenic acid and monofluoroarsenic acid.

This application is a continuation-in-part of our copending application Ser. No. 848,119, filed Aug. 6, 1969 and now abandoned, which in turn is a continuation-inpart of our co-pending application Ser. No. 702,547, filed Feb. 2, 1968 and now abandoned.

BACKGROUND OF THE INVENTION Conventional processes for the manufacture of phosphorus pentafluoride are based on the halogen exchange of phosphorus pentachloride with arsenic trifluoride,

3-PCI 5AsF 3P F +5AsCl or on the chlorofluorination of phosphorus trifluoride,

SPF 3 +01 3PF +2PCl Both methods required extensive fractionation to separate mixed halides (PC1134, PCl F etc.) from phosphorus pentafluoride.

Fluorophosphoric acids, on the other hand, are produced from phosphorus pentoxide and hydrogen fluoride at the appropriate molar ratios:

Conventional procedures for the manufacture of arsenic pentafluoride, As-F involve the fluorination of arsenic, As, or arsenic trifluoride, AsF with elemental fluorine, F

Hexafluoroarsenic acid, HAsF is produced by reacting arsenic pentoxide, As O with anhydrous hydrogen fluoride, HF.

SUMMARY OF THE INVENTION "ice tions in the process conditions, it is possible to obtain either the acid or the pentafluoride as the sole product.

DETAILED DESCRIPTION The reaction begins upon heating a phosphorus or arsenic source and a fluorine source to above 120 C. The phosphorus or aresenic source may be phosphoric or arsenic acid or the fluorinated derivatives of these acids. The acids are preferably as pure as possible, but the reaction will occur satisfactorily using wet process phosphoric acid as well as furnace acid. Above concentration levels of 72% P 0 or 100% H AsO increasing the acid concentration does not affect the product distribution. Below these levels, a decrease in acid concentration is accompanied by a shift in product distribution from the pentafluoride to the acid. Best results are obtained using a phosphorus source having a P 0 concentration of about 65-82% or an arsenic source having a H AsO concentration of about 75-1 15% The fluorine source is a fluorosulfonate fluoride or a mixture of a fluorosulfonate and a fluoride. Any alkaline earth fluorosulfonate fluoride may be used. Calcium fluorosulfonate fluoride is preferred and may be prepared by sulfonation of calcium fluoride with dilute sulfur trioxide such as the converter gas from a sulfuric acid plant, at atmospheric pressure and ISO-350 C. Pulverized fluorospar can also be used as the calcium fluoride source. In this case sulfur trioxide at 50-200 p.s.i. pressure and ISO-350 C. is necessary to compensate for the lower reactivity of the mineral.

A mixture of a fluorosulfonate and a fluoride may be used in place of the fluorosulionate fluoride. The cation of the fluorosulfonate and of the fluoride may be any of the alkali or alkaline earth metals. It is not necessary that the same cation be used for the fluoride and for the fluorosulfonate. Thus, examples of suitable mixtures would be NaF+NaFSO NaF +Ca(FSO KF-I-NaFSO CaF +Ba(FSO CaF +Ca('FSO etc. We prefer to use approximately equimolar amounts of fluoride and fluorosulfonate, however, the proportions may be varied widely without negative eflect.

The molar ratio of phosphorus or arsenic source to fluorine source may vary from 1:2 to 1:8. At ratios of 1:2 to 1:4, the product is predominantly the acid. At ratios of 1:4 to 1:5 substantial amounts of both acid and pentafluoride appear as product and at ratios of 1:5 to 1:8 the pentafluoride predominates. These ratios apply to a batch process where the phosphorus or arsenic source is premixed With the fluorine source and then heated. In a continuous process the phosphorus or arsenic source is introduced to a reactor containing a heated stirred bed of the fluorine source. Conditions are such in a continuous process of this type that substantial amounts of both products are obtained at all concentrations of about 1:2 to 1:8. Most eflicient utilizaion of raw materials occurs at ratios of about 1:4 to 1:6.

The reaction begins at about C. We prefer to run the reaction at between -220 C. using a phosphorus source or between 230-270 C. using an arsenic source, but in no event, should the temperature be above 350 C. or reactant decomposition will occur. The generalized reactions can be expressed by:

other acids H XO4 M F M FSO;

where X is phosphorus or arsenic, M is an alkaline earth metal, preferably calcium, and M and M are alkali or alkaline earth metals, preferably calcium, sodium or potas- Completion of the reaction was achieved within one hour sium. M and M may be identical cations. as indicated by constant pressure. The volatile reaction The volatilized fluorine containing products are collected product was allowed to expand from the hot reactor into and cooled to about -40 C. to condense the acids and an evacuated cold (-196 C.) cylinder. A total of 15.8 g. the remaining gas is passed to suitable storage facilities. was collected and fractionated at 40 C. into 5.8 g.

As stated above, product distribution may be changed phosphorus pentafluoride and 9.5 g. hexafluorophosphoric by varying the concentration of the feed acid or the ratio acid. The actual HPF concentration in the liquid was of reactants. Product distribution may also be changed by 73.1%, determined as nitron hexafluorophosphate. injecting water into the reactor off-gas. The addition of Exam 1 HI approximately 2 moles of water per mole of phosphorus or arsenic source will produce acid product exclusively. The e n between 0-200 111018 calcium fillOfOSulfO- A similar result may be obtained by passing the off-gas nate fluoride g-) and 0.100 mole 72.4% P 0 phosinto a cool (less than 40 C.) dilute pool of the desired phoric acid (9.8 g.) produced, after treatment according acid. In the case of HAs'F the pool acid concentration to Example 11, of mixture of equal Parts difiuoroshould be kept below 85% HAsF preferably about 75%, 5 and hexafluorophosphol'ic acids The amount of P by adding H O; in the case of HPF the pool acid concenphorus pentafiuoride was less than 1.0 g.

EXAMPLES IV-VIII Procedure as in Example II- Ex. Phosphorous source Fluorine source Products H P04(82% P205), 0.1 mole, 8.6 CaF(FS0 0.3 mole, 47.5 g PF5, 4.6 g--.-.- Fo' Hz0, 8-3 g- V H1304(72.4% PzO5),0.1 mole, 9.8 CaF(FSO;), 0.2 mole, 31.6 g PF5, 1.0 g im- 20, 6-1 3- a d HPOzFz, 61 VI Hi04(72.4% Pz05),0.1 mole, 9.8 CaF, 0.15 mole, 11.7 g. and Ca- PF 5.3 g HPFu'2 20, 9-4 gvn 11 150472 47 E05) 64 g B ?6' '5 1 0;' PF. 36g nrrvzmo 5.6 g. vIIiIIII H:P03F, 10g -l.- III.'.' oaF Fso ,'1o' .IIIIIIIIII PF5:4.6 II: HPFl 2 :8- gtration should be kept below 80%, preferably below 75% Example 1X HPFB' It Is also Posslble to produce and Calcium fluorosulfonate fluoride (48.6 g.) and 100% phorus penta-fluorrde as the sole product. this emllq H AsO (14.2 g.) were mixed thoroughly in a mortar and ment of our invention the volatllrzed fluorine-containing placed in an aluminum cylinder. After evacuation, the products are colected and the pentafluoride recovered as actor was heated to A pressure of 200 P's-i. P The aclds prodllced recycled to f veloped. Volatile material was allowed to expand through tron process after blending with polyphosphorrc ac1d or a Teflon tube (.1/2 X 12 maintained at into P Pentoxlde' ThePmPcrtwnsPf hexafluorophos' a cylinder cooled with ice. The remaining gaseous mateac1d to the y ac1d or Pentoxlde Should be such rial was condensed in another cylinder maintained at to give a molar fluorine/phosphorus ratio of 1.5 to 2.5, preferably 2.0. The polyphosphorlc 8014 Should have a After completion of the run, the Teflon tube contained P205 equlvalent of from about 70 to Preferably from 40 3.6 g. of solid hexafiuoroarsenic acid monohydrate. The about to P2O5' first cylinder (0 C.) contained 5.2 g. of liquid hexafluoro- The refictloP f Polyphosphorlc ac1d f hexafluofo' arsenic acid (88% HAsF and the second cylinder phosphoric ac1d 1s moderately exotherm1c. The reaction C 5 f arsenic penta fluoride temperature should be prevented from rising above about 1 80C. The reaction is preferably run at a temperature in Examp e X the range of about 40 to 60 C. The resulting liquid is An equimolar mixture of potassium fluoride (29.2 g.) then recycled to the fluorination step. and potassium fluorosulfonate (69.0 g.) was heated to The following examples show specific embodiments of 150 C. in an aluminum reactor while stirring. our invention and, as such, are not intended to be limiting. Arsenic acid was injected as an 85 H3ASO4 solution in water (59.1 g.). The temperature was increased to 250 C. over a three-hour period and the volatile mate- Calcium fluoride (45.0 g.) was pl c 111 a vel'tlcal rial passed into liquid hexafluoroarsenic acid from a 1 x 20-1n. glass tube equlpped wl a frltted disk to q previous run. The temperature of the stirred acid pool the P m enm'e tube was heated to Whlle was kept at 0 C. by external cooling. Water was added 8 Introduced at bottom of the tube to periodically to keep the hexafluoroarsenic acid concenachleve fluldlzatlon After heatmg for one hour to assure tration below 80%. A total of 48.2 g. of hexafluoroarsenic dryness of the charge, hot sulfur trioxide gas was blended acid on a 100% basis was obtained. into the air sweep to maintain a 10% (vol.) S0 concentration. The absorption of sulfur trioxide was quantitative Example XI during the first tWO Thereafter, P Of the 3 Technical grade arsenic acid (47.0 g.) containing 75 Example I began to pass through the reactor. The reaction was con- H AsO was concentrated by evaporation to 100% tinued until 46.0 g. S0 had been absorbed which required H ASO as injected gradually into a stirred bed of an additional hour. The dry air sweep was maintained for barium fluorosulfonate fluoride (210.0 g.) while heating another 110111 to remove all Physically-absorbed 3- The to maintain 250 C. The volatile reaction product was final Product contained mole 3 P mole of Cfl zpassed into a stirred pool of 41% I-LAsF which was cooled The material was moderately hygroscopic and had to be by an ice bath. Residual gaseous product from the reactor stored in a dry atmosphere to avoid hydrolysis. was swept into the receiving vessel by a stream of dry Example 11 air. At the end of the operation, the hexa-fluoroarsenic acid concentration in the pool had increased to 85 This TO 0.300 mole of calcium fiuorosulfonate fluoride (47.5 corresponded to a 7 5% conversion of the employed 8). P p actlol'diflg to p 1 above, was added arsenic acid to hexafluoroarsenic acid. 0.100 mole (9.8 g.) of 72.4% P 0 phosphoric acid. The mixture was blended thoroughly in a mortar while exclud- Examp 1e XII ing moisture. After transfer to an aluminum cylinder and Twelve kg. of hexafluorophosphoric acid containing evacuation, the reaction was started by heating to 200 C. 7075% HPF were placed in a polyethylene-lined reactor 5 and stirred rapidly. A total of 9.5 kg. of phosphorus pentoxide was added gradually over a 3-hour period while cooling to maintain the temperature below 50 C. The resulting liquid was then fiuorinated by spraying it into a stirred bed of 65.0 kg. of calcium fluorosulfonate fluoride and heating to ISO-200 C. The liberated gas was passed through a dust collector into a fractionation column at 22 p.s.i.a. Maintaining the top temperature at 10 C. and the bottom at 75 C. produced 17.2 kg. of phosphorus pentafluoride and 12.0 kg. of hexafluorophosphoric acid (70-75% HPF Example XIII Polyphosphoric acid (11.4 kg.) containing 82-84% P was added slowly to 12.0 kg. of hexafluorophosphoric acid in a polyethylene-lined vessel while stirring rapidly. The temperature increased from 25 to 62 C. No cooling was applied. The resulting liquid produced, on fluorination with 65.0 kg. of calcium fluorosulfonate fluoride according to the procedure outlined in Example X II, a total of 14.0 kg. of phosphorus pentafluoride and 18.1 kg. of hexafluorophosphoric acid.

We claim: 1. A process for the preparation of PF and HP=F which comprises:

at temperatures in the range of 120-350 C., reacting a fluorine source selected from the group consisting of (a) alkaline earth fluorosulfonate fluorides, (b) alkali metal fluorosulfonate-fluoride mixtures, (c) mixtures of (a) and (b), and ((1) mixtures of alkali metal or alkaline earth fluorides with either (a), (b) or (c); with a source of phosphorus selected from the group consisting of phosphoric acids and fluorinated derivatives thereof, and recovering evolved gases containing said PF and said H PF the molar reactant ratio of said phosphorus source to said fluorine source being in the ratio of about 1:2 to about 1:8.

2. The process of claim 1, wherein said molar reactant ratio is within the range of about 1:4 to about 1:6 and said reactant temperature is within the range of about 180-220" C.

3. The process of claim 1, wherein said fluorine source is calcium fluorosulfonate fluoride.

4. The process of claim 2, wherein said fluorine source is calcium fluorosulfonate fluoride.

5. The process of claim 3, wherein said process is a batch process and the proportion of HPF in said evolved gases is increased by employing a molar reactant ratio of about 1:2 to 1:4.

6. The process of claim 3, wherein the proportion of HPF derived from said evolved gases is increased by employing a phosphorus source with a concentration of 6 less than 72% P 0 said proportion of HPF increasing as the P 0 concentration is decreased.

7. The process of claim 1, wherein the PF in the evolved gases is hydrolyzed by contact with at least about 2 moles of water per mole of P in said gases, so as to recover substantially only HPF 8. The process of claim 7, wherein said hydrolyzation is accomplished by passing said evolved gases into a cool aqueous pool, containing HPF in a concentration below about 80%.

9. The process of claim 8, wherein the HPF concentration of said pool is below 75%.

10. The process of claim 1, wherein said phosphorus source has a concentration of about -82% P 0 11. The process of claim 10, wherein the proportion of PF in said evolved gases is increased by employing a phosphorus source with a concentration greater than about 72% P 0 12. The process of claim 11, wherein said process is a batch process and the proportion of PF in said evolved gases is increased by employing molar reactant ratios of 1:5 to 1:8.

13. The process of claim 1, wherein it is desired to enhance the amount of PF recovered, which comprises:

(i) cooling said evolved gases sufiiciently to obtain a condensation product containing HPF and separating the gaseous PF (ii) at a temperature below about 80 C., contacting said condensation product with a P 0 source selected from the group consisting of P 0 or phosphoric acid having a P 0 concentration of about -90%, wherein the ratio of F in said condensation product to P in said P 0 source is within the range of about 1.5 :l to about 2.5 :l, to obtain a liquid feed useful for said phosphorus source, and

(iii) recycling said liquid feed for further reaction with said fluorine source.

14. The process of claim 13, wherein said condensation of (ii) is conducted at a temperature about 40-60 C.

15. The process of claim 14, wherein said P 0 source is a polyphosphoric acid with a concentration of about 82-84% P 0 16. The process of claim 15, wherein said fluorine source is calcium fluorosulfonate fluoride.

17. The process of claim 16, wherein the F to P atom ratio of (ii) is about 2:1.

References Cited UNITED STATES PATENTS 3,216,799 11/1965 Olstowski 23205 OSCAR R. VERTIZ, Primary Examiner G. ALVARO, Assistant Examiner UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 2221.. Dated ctober 30 1973 Inventor) Robert A. wiesboeck et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Abstract, line 18, "nad" should read and Column 3, EXAMPLES IV-VIII under Ex. line 1 should read IV and-under Phosphorus source, line 1, "H P0 should read *H PO Column 3, line 33, "colected" should read collected Example I, line 53, "l"-should read l- Signed and sealed this 3rd day of September 1974.

(SEAL) Attest:

MCCOY M. GIBSON, JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents FORM PC4050 uscoMM-oc 60376-P69 W U 5l GOVFRNHENT PRINTING OFFICE IQ, 0-566-33L 

